The present invention relates to an electric machine with permanently excited inner stator.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Electric machines are known which include an outer stator and an inner stator, between which a rotor is arranged. Electric machines can be designed as synchronous machines, in particular three-phase synchronous machines. Such three-phase synchronous machines can be operated as a motor or as a generator, for example, and are steadily gaining in significance. Permanently excited three-phase synchronous machines are known in the art and include permanent magnets arranged on the rotor or the armature. Permanent magnets have the disadvantage of limited operating temperatures. For this reason, magnets made of rare earths are increasingly used because of their higher operating temperatures in comparison with permanent magnets which are normally used. A disadvantage of rare-earth magnets is their high price. Moreover, cooling of the rotor and/or the permanent magnets, e.g. by water cooling, can only be achieved at high cost.
It would therefore be desirable and advantageous to provide an improved electric machine, in particular synchronous machine which obviates prior art shortcomings and which is simple in structure and yet reliable in operation in an economical and effective manner.